Immunocytochemical localization of cyclic GMP, cGMP-dependent protein kinase, calmodulin and calcineurin in Paramecium tetraurelia.

The localization of cGMP, cGMP-dependent protein kinase, calmodulin and the calmodulin-binding protein calcineurin in Paramecium tetrauelia cells has been examined with immunocytochemical methods. These molecules appeared to be localized to a large extent in the cilia of this protozoan. To ascertain that antibodies had access to all cellular compartments we have used three different preparations for immunocytochemistry: (i) with 'whole cell' preparations immunofluorescent staining for the four molecules was mainly visible in the cilia; (ii) in 'deciliated' Paramecium, staining for cGMP and calmodulin was found in regular patterns on the cell surface most likely representing kinetosomes; (iii) using 'sectioned cells', additional cytoplasmic calmodulin appeared to be associated with glycogen particles as evidenced by the disappearance of the granular staining pattern after preincubation with alpha-amylase. In contrast, cGMP, cGMP-dependent protein kinase and calcineurin fluorescence was only very weak and diffuse in cell bodies. No nuclear fluorescence was detectable after staining with any of the antibodies. Because of the colocalization of cGMP, cGMP-dependent protein kinase, a guanylate cyclase-calmodulin-complex, and calcineurin in cilia from Paramecium, an involvement of these components in the regulation of ciliary activity is discussed.